1. Field of the Invention
The present invention relates to a safety hypodermic syringe and more particularly, to such a safety hypodermic syringe that prevents breaking of the breakable front wall of the barrel accidentally during transportation.
2. Description of the Related Art
A hypodermic syringe is an important medical instrument adapted for use to inject or withdraw liquid medicines. In recent years, the spreading of AIDS and many other diseases that are difficult to treat causes many contamination accidents. In order to prevent contamination, safety hypodermic syringes are developed. A safety hypodermic syringe is known comprising a needle assembly, a medicine barrel, a plunger, and an outer barrel. The needle assembly is fastened to the front side of the medicine barrel. The plunger is axially movably coupled to the medicine barrel and mounted with the medicine barrel inside the outer barrel. After the service of the hypodermic syringe, the plunger is pulled backwards to carry the needle cannula or the needle assembly backwards to the inside of the medicine barrel. This design of safety hypodermic syringe is functional, however it has a complicated structure and comprised of a big number of parts, resulting in a high manufacturing cost.
Taiwan Patent Publication No. 540385, issued on Jul. 1, 2003, discloses a safety hypodermic syringe entitled “Two Piece Type Retractable Safety Hypodermic Syringe”. According to this design, the safety hypodermic syringe comprises a barrel, a plunger inserted into the barrel, a needle holder provided at the front side of the barrel to hold a needle, and a block with a through hole installed in the needle holder. The barrel has a tear groove on the front wall around the needle holder. After engagement of the head of the plunger with the needle holder, the plunger is pulled backwards to break the tear groove, causing the needle holder and the needle to be carried with the plunger backwards to the inside of the barrel. According to this design, the thin tear groove on the front wall of the barrel may be broken accidentally during injection or transportation of the safety hypodermic syringe, thereby causing a leakage of the fluid medicine.
Further, according to conventional designs, a residual amount of the applied liquid medicine will be left in the tubular front neck of the barrel and the hub of the needle assembly after the stopper has been pushed to the front limit position and stopped at the front wall of the barrel.
Therefore, it is desirable to provide a safety hypodermic syringe that eliminates the aforesaid drawbacks.